Material design for the encapsulation of additives and release

ABSTRACT

Embodiments provide a method for controlled release of a cement additive for use in a wellbore. The method includes the steps of mixing an aramide capsule with a cement slurry to form an additive-containing slurry, and introducing the additive-containing slurry into the wellbore. The aramide capsule is formed by interfacial polymerization where an aramide polymer forms a semi-permeable membrane encapsulating the cement additive.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a divisional application of U.S. patent applicationSer. No. 16/230,391, filed on Dec. 21, 2018, which claims the benefit ofand priority to U.S. Provisional Patent Application No. 62/612,754,filed on Jan. 2, 2018; the disclosures of which are incorporated hereinby reference in their entireties.

BACKGROUND 1. Technical Field

Disclosed are compositions and methods for use with cement.Specifically, disclosed are compositions and methods for controlling adownhole environment during cement operations.

2. Related Art

In many wellbores, cement can be used to form a layer between a casingand the formation. Delivery of additives to the cement can beproblematic for a variety of reasons. First, the additives must be mixedwith the cement slurry and delivered along with the slurry to thedownhole location. Second, the additives must survive intact at theextreme downhole conditions in order to impart their additiveproperties. Third, controlling the release rate of an additive can bedifficult in a downhole environment.

Encapsulation-based systems are of interest in the oil and gas industryin applications such as chemical additive preservation, small moleculerelease, particle delivery, and self-sealing materials. Many methods areused to encapsulate relevant chemical additives for the controlledrelease of contents. Example capsulation materials include polymericcoatings, inorganic shells, and mesoporous materials.

When placing cement in a wellbore, a multitude of additives (usually inlarge quantities) are considered and added to the slurry in order tomeet a variety of functional needs suitable for diverse wellboreconditions. However, using large quantities of certain additives (forexample, retarders and fluid loss control agents) may destabilize theslurry at the surface even before introducing the slurry into thewellbore.

SUMMARY

Disclosed are compositions and methods for use in cement slurries.Specifically, disclosed are compositions and methods for controlling adownhole environment during cement operations.

Embodiments provide a system for the controlled release of encapsulatedcargo that utilizes engineered features of permeable polymeric shellwalls. Using vesicles or capsules, cement additives can be deliveredwithout physical or chemical modification. Various cement formulationscan be designed utilizing numerous combinations of vesicles with variousencapsulants. Vesicle systems are particularly useful for deliveringagents such as chemical additives and small molecules to providebeneficial interactions in cement slurry applications. Such cementslurry applications include chemical delivery and controlled release ofchemical additives during placement of a slurry downhole.

In a first aspect, a method for encapsulating a cement additive for usein a wellbore includes the step of mixing a continuous solvent and asurfactant to produce a continuous phase. The method includes the stepof mixing a dispersed solvent, a dispersed monomer, and the cementadditive to produce a dispersed phase. The dispersed solvent and thecontinuous solvent are immiscible. The method includes the step ofmixing the continuous phase and the dispersed phase to form a mixturehaving an emulsion such that the dispersed phase is dispersed asdroplets in the continuous phase. An interface defines the droplets ofthe dispersed phase dispersed in the continuous phase. The methodincludes the step of adding a crosslinker to the mixture. The methodincludes the step of allowing an aramide polymer to form on theinterface of the droplets, such that the aramide polymer forms asemi-permeable membrane around a core. The core contains the dispersedphase, such that the semi-permeable membrane around the core forms thearamide capsule. The method includes the step of allowing the aramidecapsule to settle from the mixture. The method includes the step ofseparating the aramide capsule from the mixture using a separationmethod.

In certain aspects, the dispersed solvent can include water, ethanol,and methanol. In certain aspects, the dispersed monomer includes anamine group. In certain aspects, the dispersed monomer can includeethylenediamine, meta-phenylenediamine, para-phenylenediamine, andhexamethylenediamine. In certain aspects, the continuous solvent caninclude oil, mineral oil, cyclohexane, and chloroform. In certainaspects, the crosslinker can include 1,3,5-benzenetricarbonyltrichloride and sebacoyl chloride. In certain aspects, the cementadditive is water-soluble and can include sealing reagents, anti-gasmigration additives, high-temperature retarders, fluid-loss additives,accelerators, and superplasticizers.

In a second aspect, a method for controlled release of a cement additivefor use in a wellbore includes the step of mixing an aramide capsulewith a cement slurry to form an additive-containing slurry. The methodincludes the step of introducing the additive-containing slurry into thewellbore. The aramide capsule is formed by the step of mixing acontinuous solvent and a surfactant to produce a continuous phase. Thearamide capsule is formed by the step of mixing a dispersed solvent, adispersed monomer, and the cement additive to produce a dispersed phase.The dispersed solvent and the continuous solvent are immiscible. Thearamide capsule is formed by the step of mixing the continuous phase andthe dispersed phase to form a mixture having an emulsion such that thedispersed phase is dispersed as droplets in the continuous phase. Aninterface defines the droplets of the dispersed phase dispersed in thecontinuous phase. The aramide capsule is formed by the step of adding acrosslinker to the mixture. The aramide capsule is formed by the step ofallowing an aramide polymer to form on the interface of the droplets,such that the aramide polymer forms a semi-permeable membrane around acore. The core contains the dispersed phase, such that thesemi-permeable membrane around the core forms the aramide capsule. Thearamide capsule is formed by the step of allowing the aramide capsule tosettle from the mixture. The aramide capsule is formed by the step ofseparating the aramide capsule from the mixture using a separationmethod.

In certain aspects, the method further includes the step of allowing thecement additive to permeate from the core through the semi-permeablemembrane to the cement slurry. The method further includes the step ofallowing the cement additive to have a beneficial interaction with thecement slurry. In certain aspects, the method further includes the stepof allowing the additive-containing slurry to set to form a hardenedcement. The aramide capsule is embedded in the hardened cement. Themethod further includes the step of allowing the cement additive topermeate from the core through the semi-permeable membrane to thehardened cement. The method further includes the step of allowing thecement additive to have a beneficial interaction with the hardenedcement. In certain aspects, the hardened cement has an unconfinedcompression strength ranging from about 3,000 pounds per square inch(psi) to about 3,400 psi. In certain aspects, the method furtherincludes the step of allowing the additive-containing slurry to set toform a hardened cement. The aramide capsule is embedded in the hardenedcement. The method further includes the step of allowing thesemi-permeable membrane to burst such that the cement additive isreleased from the aramide capsule and migrates through the hardenedcement. The method further includes the step of allowing the cementadditive to have a beneficial interaction with the hardened cement. Incertain aspects, the hardened cement has an unconfined compressionstrength ranging from about 3,000 psi to about 3,400 psi.

In certain aspects, the dispersed solvent can include water, ethanol,and methanol. In certain aspects, the dispersed monomer includes anamine group. In certain aspects, the dispersed monomer can includeethylenediamine, meta-phenylenediamine, para-phenylenediamine, andhexamethylenediamine. In certain aspects, the continuous solvent caninclude oil, mineral oil, cyclohexane, and chloroform. In certainaspects, the crosslinker can include 1,3,5-benzenetricarbonyltrichloride and sebacoyl chloride. In certain aspects, the cementadditive is water-soluble and can include sealing reagents, anti-gasmigration additives, high-temperature retarders, fluid-loss additives,accelerators, and superplasticizers. In certain aspects, the aramidepolymer of the aramide capsule is present in the additive-containingslurry at a concentration of at least about 3% by weight of cement. Incertain aspects, the cement additive is tethered in the core of thearamide capsule via site-isolation of a water-soluble polymer.

In a third aspect, an aramide capsule for use in a cement environmentincludes a semi-permeable membrane including an aramide polymer. Thesemi-permeable membrane forms a shell with a core, such that the corecontains a cement additive. The semi-permeable membrane is operable toallow the cement additive to permeate from the core through thesemi-permeable membrane to the cement environment. The aramide capsuleincludes the cement additive. The cement additive is operable to imparta beneficial interaction on the cement environment. The aramide polymerincludes subunits derived from a monomer including a di-functional aminogroup and subunits derived from a crosslinker including an acylchloride.

In certain aspects, the aramid capsule further includes a linearpolymer. The linear polymer is water-soluble and is operable to tetherthe cement additive in the core via site-isolation. In certain aspects,the linear polymer can include polyethylene glycols, polystyrenes,polyethylene imine, polyvinyl alcohols, and polyvinylpyrrolidone. Incertain aspects, the monomer can include ethylenediamine,meta-phenylenediamine, para-phenylenediamine, and hexamethylenediamine.In certain aspects, the crosslinker can include 1,3,5-benzenetricarbonyltrichloride and sebacoyl chloride. In certain aspects, the cementadditive is water-soluble and can include sealing reagents, anti-gasmigration additives, high-temperature retarders, fluid-loss additives,accelerators, and superplasticizers.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other features, aspects, and advantages of the scope willbecome better understood with regard to the following descriptions,claims, and accompanying drawings. It is to be noted, however, that thedrawings illustrate only several embodiments and are therefore not to beconsidered limiting of the scope as it can admit to other equallyeffective embodiments.

FIG. 1 is a photographic representation of the aramide capsules embeddedin a cement slurry, as imaged by optical microscopy at ambientconditions.

FIG. 2 is a graphical representation showing ultraviolet/visible(UV/Vis) absorbance of the encapsulant released from the aramide capsulesamples over time.

FIG. 3 is a photographic representation of the aramide capsule, asimaged by optical microscopy at ambient conditions.

FIG. 4 is a graphical representation showing viscosity of the cementslurry having the encapsulant within the aramide capsule samples ofvarying monomer concentration.

FIG. 5 is a graphical representation showing viscosity of the cementslurry having aramide capsule samples over time.

FIG. 6 is a graphical representation showing unconfined compressionstrengths of cement samples.

In the accompanying Figures, similar components or features, or both,may have a similar reference label.

DETAILED DESCRIPTION

While the scope of the apparatus and method will be described withseveral embodiments, it is understood that one of ordinary skill in therelevant art will appreciate that many examples, variations andalterations to the apparatus and methods described here are within thescope and spirit of the embodiments.

Accordingly, the embodiments described are set forth without any loss ofgenerality, and without imposing limitations, on the embodiments. Thoseof skill in the art understand that the scope includes all possiblecombinations and uses of particular features described in thespecification.

The compositions and methods are directed to cement additive deliverysystems. Advantageously, the composition and methods described here canmitigate gas migration and the formation of micro-annuli in cementslurries. Advantageously, the compositions and methods can increase thecompression strength following the thickening time, decreasing thepermeability of the hardened cement. Advantageously, the compositionsand methods described can provide high-temperature cement additives thatenable the delivery of cement additives at controlled release after acement slurry has been placed in a wellbore.

Chemical additives are frequently used for designing cement slurryformulations to produce reliable cement sheaths for well construction.However, the chemical additives may not properly function at wellboreconditions where the extreme temperature and pressure may alter thedesired chemical functionalities of the additives. Advantageously, thechemical additives (for example, a dispersant or an accelerator) can beencapsulated by methods incorporating interfacial polymerization, suchthat the chemical additives are placed within a hollow polymer shell andshielded from extreme wellbore conditions. The shells are designed forthe delayed release of the chemical additives providing molecular andtemporal control for field applications. Similar to chemical additives,interfacial polymerization can be employed for encapsulating engineeredadditives. The engineered additives can also be placed within the hollowpolymer shell for the controlled release of the additives in thewellbore.

As used throughout, “capsule” refers to one or more particles ofparticular combination of semi-permeable membrane and cement additive. Areference to the singular capsule includes multiple particles. Areference to the plural capsules is a reference to compositions ofdifferent semi-permeable membranes.

As used throughout, “shell” refers to an enclosure that completelysurrounds a core.

As used throughout, “semi-permeable” means that certain components areable to pass through. The ability for a component to pass through asemi-permeable membrane depends on the size and charge of the component.

As used throughout, “shearing rate” refers to the mixing speed whenforming the emulsion-based capsules.

As used throughout, “beneficial interaction” means the cement additiveimparts a benefit to the cement slurry or hardened cement or theproperties of the cement slurry or hardened slurry. “Benefit” as usedhere means a positive impact. Non-limiting examples of beneficialinteractions include sealing the cement to mitigate micro-annuliformation of set cements during the lifetime of the well and releasingcement additives in a controlled fashion as the slurry is mixed with theadditives or as the mixed slurry is introduced downhole. Non-limitingexamples of beneficial interactions also include gas migration controland enhancing mechanical properties of set cement.

As used throughout, “cement environment” refers collectively any stageof the cement process and includes both the cement slurry and thehardened cement.

As used throughout, “immiscible” means not forming a homogeneous mixturewhen two or more solvents are added together. Immiscible solvents mayform an emulsion. Non-limiting examples of immiscible solvents includeoil and water, and cyclohexane and water.

As used throughout, “wellbore” refers to a hole drilled into asubsurface formation of the earth, where the subsurface formation cancontain hydrocarbons. The wellbore can have a depth from the surface anda diameter and can transverse the subsurface formation vertically,horizontally at a parallel to the surface, or at any angle betweenvertically and parallel.

As used throughout, “aramide” refers to an aromatic polyamide. Termssuch as “aramids,” “aramides,” “polyaramids,” “polyaramides,” “aramidpolymers,” “aramide polymers,” and “aromatic polyamides” are usedinterchangeably. Commercial examples of aramides include para-aramidessuch as Kevlar® (available from Dupont®, Wilmington, Del.), Technora®(available from Teijin Aramid USA, Inc, Conyers, Ga.), Twaron°(available from Teijin Aramid USA, Inc, Conyers, Ga.), and Heracron®(available from Kolon Industries, Inc., Gwachon, Korea), andmeta-aramides such as Nomex® (available from Dupont®, Wilmington, Del.)and Teijinconex® (available from Teijin Aramid USA, Inc, Conyers, Ga.).A para-aramide is an aramide where the polymer chain is connected viathe para positions of an acyl group subunit or functional group. Ameta-aramide is an aramide where the polymer chain is connected via themeta positions of an acyl group subunit or functional group.

The aramide capsule can be composed of a cement additive encapsulated bya semi-permeable membrane. The aramide capsule can have a specificgravity of between 1.0 and 1.5, alternately of between 1.2 and 1.4. Thespecific gravity of the aramide capsule is comparable to the specificgravity of aramides.

The cement additive can be any cement additive imparting a beneficialinteraction to the cement environment. Cement additives can includesealing reagents, anti-gas migration additives, accelerators,high-temperature retarders, fluid-loss additives, accelerators,superplasticizers, and combinations of the same. Sealing reagents can beany material capable of self-sealing fractured cement. Sealing reagentscan include polymers, salts, rubber, water, latexes, epoxy, silicones,and combinations of the same. Sealing reagents can include a polymerwith a T_(g), that is, a glass transition temperature where polymersbecome soft and flowable. In cases where the cement is compromised withmicro-cracks, these sealing reagents self-seal the hardened cement toincrease the workable lifetime of the well. In some embodiments, thecement additive is in a free-flowing powder form and is added, eitherwetted or not, to the dry mix when producing a slurry formulation. Insome embodiments, the cement additive is water-soluble and can bedissolved in the dispersed solvent to form a dispersed phase.

The semi-permeable membrane can be an aramide polymer that issemi-permeable. The semi-permeable membrane can be a crosslinked aramidepolymer. The aramide polymer can be formed through a polycondensationreaction. The polycondensation reaction can form other polymers suitablefor the semi-permeable membrane, such as polyesters, polyurethanes, andpolyureas. Examples of the aramide polymer that can form thesemi-permeable membrane include polyamides, aramides, and combinationsof the same. The semi-permeable membrane forms a shell encapsulating acore. The core contains the cement additive. The core can be a liquidcore. Advantageously, aramides have high-temperature resistance andballistic-rated strength. The semi-permeable membrane can be heatresistant up to temperatures of 400 deg. C. The semi-permeable membranecan maintain the integrity of the cement additive, resist chemicalcontamination of the cement additive, and keep the cement additive fromdegrading in the presence of the cement slurry until desired. Thesemi-permeable membrane can allow the cement additive to permeate fromthe core to outside the cement additive capsule. The cement additive canpermeate through the semi-permeable membrane via osmosis, fluiddisplacement, or mechanical rupture. The semi-permeable membraneprovides for a controlled release rate of the cement additive. Theextent of crosslinking of the aramide polymer can determine thepermeability of the semi-permeable membrane. The release rate can becontrolled by adjusting the permeability of the semi-permeable membrane.

The aramide capsule can be formed through the method of interfacialpolymerization. In the process of interfacial polymerization twoimmiscible fluids, such as a continuous phase and a dispersed phase, areblended together until the dispersed phase is dispersed as droplets inthe continuous phase forming an emulsion. At least one phase contains amonomer and a crosslinker can be included in the other phase and thearamide polymer can form on the interface between the dispersed dropletand the continuous phase forming a shell around the droplet of thedispersed phase, such that the dispersed phase is captured within theshell. The shell formed through interfacial polymerization is thesemi-permeable membrane.

The continuous phase can include a continuous solvent and a surfactant.In at least one embodiment, the continuous phase includes a crosslinker.In at least one embodiment, the crosslinker is added after the dispersedphase and the continuous phase have been blended. The continuous solventcan be any polar or non-polar solvent immiscible with water. Non-polarsolvents suitable for use as the continuous solvent include oil, mineraloil, cyclohexane, chloroform, and combinations of the same. Thecrosslinker can be any acyl chloride monomer. Examples of crosslinkersinclude 1,3,5-benzenetricarbonyl trichloride, sebacoyl chloride, andcombinations of the same. The surfactant can include sorbitan esters,polyethoxylated sorbitan esters, and combinations of the same.

The dispersed phase can include a dispersed solvent, a dispersedmonomer, and the cement additive. The dispersed solvent can be anyaqueous solvent that is immiscible with the continuous solvent. In atleast one embodiment, the dispersed solvent can include water. Thedispersed monomer can be any water-soluble diamine. The dispersedmonomer can be any diamine monomer including a di-functional aminogroup. Examples of dispersed monomers include ethylenediamine,meta-phenylenediamine, para-phenylenediamine, hexamethylenediamine, andcombinations of the same. The cement additives can be heterogeneous orsolubilized. The cement additives can be blended into the dispersedphase. In at least one embodiment, the cement additives can be dissolvedin the dispersed solvent to form the dispersed phase. In at least oneembodiment, the dispersed phase can include a metal oxide.

The continuous phase solvent and the dispersed phase solvent can beselected such that the two fluids are immiscible with each other.

The continuous monomer and the dispersed monomer can be selectedtogether in consideration of the properties of the aramide polymer thatforms the semi-permeable membrane. The continuous monomer and thedispersed monomer can be selected to produce polyamides, aramides,polyesters, polyurethanes, polyureas, and combinations of the same. Inat least one embodiment, the dispersed monomer can includeethylenediamine, meta-phenylenediamine, para-phenylenediamine, andcombinations of the same. The crosslinker can include1,3,5-benzenetricarbonyl trichloride. In at least one embodiment, thedispersed monomer can include hexamethylenediamine and the crosslinkercan include sebacoyl chloride.

The amount of crosslinker added to the continuous phase can controlpermeability of the semi-permeable membrane. More than one continuousmonomers or dispersed monomers can be used to control permeability ofthe semi-permeable membrane.

The continuous phase and the dispersed phase are blended together untilthe dispersed phase is dispersed as droplets in the continuous phaseforming an emulsion. Depending on the volume of each phase awater-in-oil (w/o) emulsion or an oil-in-water (o/w) emulsion can beformed. The droplets can have different shapes including spheres, rods,fibers, and combinations of the same. The size of the droplets of thedispersed phase can be between 50 nanometers (nm) and 50 microns (μm),alternately between 100 nm and 1 μm, alternately between 1 μm and 10 μm,and alternately between 10 μm and 50 μm. The size and shape of thedroplets of the dispersed phase in the continuous phase can becontrolled by the shearing rate, the use of laminar flow, the dispersedsolvent, the density of the dispersed solvent, the rate of blending ofthe continuous solvents and dispersed solvent, and viscosity of thedispersed phase. In at least one embodiment, laminar flow can be usedform fibers. The size of the droplets can be optimized to impart a lowrheological property to the cement slurry.

In at least one embodiment, the cement additive is insoluble in waterbut soluble in organic solvents. The continuous phase includes water asthe continuous solvent and the dispersed phase includes the organicsolvent as the dispersed solvent. Mixing the two phases may form an o/wemulsion for applications in oil-based drilling fluids.

In at least one embodiment, the crosslinker is present in the continuousphase when the two phases are blended together as a mixture and thearamide polymer begins to form as the emulsion is created. In at leastone embodiment, the crosslinker is added to the mixture after theemulsion of dispersed droplets in the continuous phase has beendeveloped.

The aramide polymer forms on the interface of the dispersed droplet andthe continuous phase creating the aramide capsules. The polymerizationreaction occurs at room temperature. The polymerization results in acovalently bonded crosslinked aramide polymer. The mixture is stirred toenhance homogeneity of the aramide polymer. In at least one embodiment,the mixture can be stirred for a period from about 24 hours to about 72hours. In at least one embodiment, the aramide capsules can settle tothe bottom of the reactor. In a next step, the aramide capsules areseparated from the liquids remaining. The separation method used toseparate the aramide capsules can be any process capable of separating aliquid and leaving behind dry capsules as a free-flowing powder.Separation methods can include decantation, filtration, centrifuging,rotary evaporation, vacuum drying, oven drying, and combinations of thesame. In at least one embodiment, the separation method leaves a liquidat the core, creating a liquid filled capsule. In at least oneembodiment, the separation method results in desiccation of the aramidecapsule removing the liquid in the core. In at least one embodiment, thedry capsules can be washed to remove any residue of the continuous phaseand then dried.

Additional reagents that can be added to the continuous phase and thedispersed phase include emulsifiers and viscosifiers. In at least oneembodiment, the emulsifier added to the continuous phase is sorbitantrioleate. In at least one embodiment, the emulsifier added to thedispersed phase is polyethoxylated sorbitan ester.

The aramide capsule can be used to provide beneficial interaction withthe cement environment. The aramide capsule is mixed with a cementslurry to form an additive-containing slurry. In at least oneembodiment, the aramide capsule can be mixed with a cement slurryaccording to the API RP 10-B standard. The aramide capsule can be mixedwith the cement slurry as a free-flowing dry powder, as liquid-filledcapsules, or as part of a liquid emulsion. The aramide capsule can beused with any type of cement slurry. In at least one embodiment, thecement in the cement slurry is hydrophilic. In at least one embodiment,the cement slurry includes a class G Portland cement. In at least oneembodiment, the cement additive is present in the cement slurry at aconcentration of between 0.05% by weight of cement (bwoc) and 5% bwoc.In at least one embodiment, the aramide polymer of the semi-permeablemembrane is present in the cement slurry at a concentration of at least3% bwoc. In at least one embodiment, two or more aramide capsules can beadded to the cement slurry, such that two or more different cementadditives are carried into the cement slurry. The aramide capsule can bemixed within the cement slurry to distribute the aramide capsule throughthe cement slurry. The additive-containing slurry can be introduced tothe formation according to any process for placing cement in a wellboreor formation. FIG. 1 is a photographic representation of the aramidecapsules embedded in a cement slurry, as imaged by optical microscopy atambient conditions.

The cement slurry sets into a hardened cement such that the aramidecapsules are embedded in the hardened cement. In some embodiments, thehardened cement including the aramide capsules exhibits an unconfinedcompression strength ranging from about 2,500 psi to about 3,500 psi atabout 350 deg. F. for about 120 hours. In other embodiments, thehardened cement including the aramide capsules exhibits an unconfinedcompression strength ranging from about 2,800 psi to about 3,500 psi atabout 350 deg. F. for about 120 hours. Still in other embodiments, thehardened cement including the aramide capsules exhibits an unconfinedcompression strength ranging from about 3,000 psi to about 3,400 psi atabout 350 deg. F. for about 120 hours. For comparison, neat cementexhibits an unconfined compression strength in similar conditionsranging from about 3,000 psi to about 4,000 psi, from about 3,400 psi toabout 3,700 psi, or from about 3,500 psi to about 3,600 psi. Also forcomparison, latex-containing hardened cement exhibits an unconfinedcompression strength in similar conditions ranging from about 1,500 psito about 2,500 psi, from about 1,800 psi to about 2,300 psi, or fromabout 1,900 psi to about 2,200 psi. In some embodiments, the hardenedcement including the aramide capsules exhibits a confined compressionstrength ranging from about 5,000 psi to about 14,000 psi at roomtemperature. In other embodiments, the hardened cement including thearamide capsules exhibits a confined compression strength ranging fromabout 9,000 psi to about 12,000 psi at room temperature.

In at least one embodiment, the cement additive permeates from the coreof the aramide capsule through the semi-permeable membrane to the cementenvironment surrounding the aramide capsule. In at least one embodiment,semi-permeable membrane of the aramide capsule can burst under thestress of the hardened cement The cement additive then migrates throughthe cement environment. After the cement additive leaves the aramidecapsules, the remaining aramide polymer of the semi-permeable membranecan impart strengthening properties to the matrix of the hardenedcement.

In at least one embodiment, the beneficial interaction of the cementadditive is to seal the cement. Sealing the cement makes the cementresistant to the influx of formation gases.

In at least one embodiment, the cement additive is tethered in the coreof the aramide capsule via site-isolation using a linear polymer. Thecement additive can be tethered to the semi-permeable membrane, tetheredwithin the semi-permeable membrane, or tethered onto the semi-permeablemembrane. In at least one embodiment, the cement additive can besite-isolated using linear polymers, such as polyethylene glycols(PEGs), polystyrenes, polyethylene imine, polyvinyl alcohols,polyvinylpyrrolidone, and combinations of the same. These linearpolymers are typically water-soluble. The side chains of these linearpolymers can be designed to contain the cement additive via chelation.Non-limiting examples of tethered cement additives include salts,accelerators, and metal catalysts. In other embodiments, these linearpolymers can be cleaved such that the cleaved molecules can travelthrough the semi-permeable membrane. For example, linear polymers havingcarboxylic acid groups can be cleaved such that the cleaved moleculehaving the carboxylic acid group may serve as a cement retarder. In someembodiments, a viscosifier can be used to site-isolate the encapsulant.

Cement ductility refers to a measure of cement reliability where cementintegrity is enhanced by making cement more elastic and ductile.Advantageously, the semi-permeable membrane of the aramide capsuleimproves cement ductility.

In at least one embodiment, the aramide capsule is in the absence of amolecular sieve.

EXAMPLE 1

A number of samples of aramide capsules were formed according to themethods described. The continuous solvent was a 4:1cyclohexane-chloroform blend. The surfactant was a 1.5% by volumesorbitan trioleate (Span-85®, Sigma-Aldrich®, St. Louis, Mo.). Thecontinuous phase included the continuous solvent and the surfactant. Thecrosslinker was 1,3,5-benzenetricarbonyl trichloride. The dispersedsolvent was water. The dispersed monomer was 1,6-diaminohexane. Thecement additive was the dispersant sulfonated acetone-formaldehydecondensate (SAFC). The dispersed phase included the dispersed solvent,the dispersed monomer, and the cement additive. SAFC has a red color,and so acted as a dye or a signaling molecule in Example 1. The SAFCallowed measurements to be taken of the release rate from the capsules.

The aramide capsules were prepared at room temperature. 25 milliliters(mL) of the continuous phase was added to 3 mL of the dispersed phase.The mixture was stirred for 15 minutes forming a w/o emulsion. After 15minutes of stirring the crosslinker was added to the mixture in anamount in milliMolars (mM) according to Table 1. For each sample, thecrosslinker was added at a rate of about 1.5 mL per minute. Stirringcontinued while the crosslinker was being added. Stirring maintained thew/o emulsion.

TABLE 1 Sample Amount of Crosslinker (mM) A 23 B 46 C 77 D 154

After 20 minutes, polymerization was stopped by filtering the solidaramide capsules. The aramide capsules were washed with 500 mL of asodium bicarbonate buffer solution (1% weight per volume (w/v), pH˜8.3).The washed aramide capsules were vacuum dried.

The aramide capsules were placed onto a microscope slide and placedunder an optical microscope with a mounted digital camera and a powersource. FIG. 1 shows an optical micrograph image 100 of the aramidecapsules 110 containing the SAFC encapsulant.

EXAMPLE 2

Polymerization of each sample formed in Example 1 was stopped atpredetermined intervals by filtering the solid aramide capsules. Eacharamide capsule sample was subjected to a multi-wash process. Eachsample was washed with diethyl ether then washed with 500 mL of a sodiumbicarbonate buffer solution (1% w/v, pH˜8.3).

UV/Vis spectrophotometry was employed to obtain absorbance curves ofSAFC for each sample. Each sample was introduced into a UV/Visspectrophotometer (λ_(max)=420 nm, from Hach, Loveland, Colo.) tomeasure absorbance. Calibration was performed by taking 1 mL calibrationsamples of each sample. After settling for a few hours, the calibrationsamples were filtered by using a 0.45 μm nylon syringe filter. Thefiltered calibration samples were introduced into the UV/Visspectrophotometer to measure absorbance of free SAFC (that is, SAFC thatis not contained in the aramide capsules) in solution. The absorbancespectrum of each sample was calibrated with the absorbance spectrum ofthe corresponding free SAFC calibration sample.

The results were shown in FIG. 2. FIG. 2 is a graphical representation200 showing UV/Vis absorbance of the encapsulant released from thearamide capsules over time. The horizontal axis represents time inminutes. The vertical axis represents UV/Vis absorbance in arbitraryunits. Square points 210 and the corresponding regression curve 212represent absorbance of Sample A in Example 1 having 23 mM ofcrosslinker. Circular points 220 and the corresponding regression curve222 represent absorbance of Sample B in Example 1 having 46 mM ofcrosslinker. Triangular points 230 and the corresponding regressioncurve 232 represent absorbance of Sample C in Example 1 having 77 mM ofcrosslinker. Reverse-triangular points 240 and the correspondingregression curve 242 represent absorbance of Sample D in Example 1having 154 mM of crosslinker.

FIG. 2 shows that the amount of dye that diffused into the supernatantwas inversely dependent on the amount of the crosslinker. FIG. 2 alsoshows that the permeability, and as a result the release rate of theencapsulant, can be controlled by the amount of crosslinker added to themixture. An increase in the concentration of the crosslinker resulted ina decrease in membrane permeability.

EXAMPLE 3

An aramide capsule was formed according to the methods described. Thecontinuous solvent was a 4:1 cyclohexane-chloroform blend. Thesurfactant was a 1.5% by volume sorbitan trioleate (Span-85®,Sigma-Aldrich®, St. Louis, Mo.). The continuous phase included thecontinuous solvent and the surfactant. The crosslinker was1,3,5-benzenetricarbonyl trichloride. The dispersed solvent was water.The dispersed monomer was 1,6-diaminohexane. The encapsulant waspolyethylenimine (PEI). The dispersed phase included the dispersedsolvent, the dispersed monomer, and the encapsulant.

The aramide capsules were prepared at room temperature. 25 mL of thecontinuous phase was added to 3 mL of the dispersed phase. The mixturewas stirred for 15 minutes forming a w/o emulsion. After 15 minutes ofstirring 40 mL of the crosslinker (0.02 M solution) was added to themixture. For each sample, the crosslinker was added at a rate of about1.5 mL per minute. Stirring continued while the crosslinker was beingadded. Stirring maintained the w/o emulsion.

After 30 minutes, polymerization was stopped by filtering the solidaramide capsules. The aramide capsules were washed with 500 mL of asodium bicarbonate buffer solution (1% w/v, pH˜8.3). The washed aramidecapsules were vacuum dried in an oven.

The aramide capsules were placed onto a microscope slide and placedunder an optical microscope with a mounted digital camera and a powersource. FIG. 3 shows an optical micrograph image 300 of the aramidecapsule 310 containing the PEI encapsulant 320.

EXAMPLE 4

A number of samples of aramide capsules were formed according to themethods described. The continuous solvent was a 4:1cyclohexane-chloroform blend. The surfactant was a 1.5% by volumesorbitan trioleate (Span-85®, Sigma-Aldrich®, St. Louis, Mo.). Thecontinuous phase included the continuous solvent and the surfactant. Thecrosslinker was 1,3,5-benzenetricarbonyl trichloride. The dispersedsolvent was water. The dispersed monomer was 1,6-diaminohexane. Thecement additive was the dispersant SAFC condensate. The dispersed phaseincluded the dispersed solvent, the dispersed monomer, and the cementadditive. SAFC has a red color, and so acted as a dye or a signalingmolecule. The SAFC allowed measurements to be taken of the release ratefrom the aramide capsules.

The aramide capsules were prepared at room temperature. 25 mL of thecontinuous phase was added to 3 mL of the dispersed phase. The dispersedphase included 130 mM of the dispersed monomer. The dispersed phaseincluded 0.5% bwoc of the SAFC encapsulant. The mixture was stirred for15 minutes forming a w/o emulsion. After 15 minutes of stirring, thecrosslinker in an amount in mM according to Table 2 was added to themixture at a rate of about 1.5 mL per minute. Stirring continued whilethe crosslinker was being added. Stirring maintained the w/o emulsion.

TABLE 2 Amount of Amount of SAFC Amount of Dispersed Encapsulant SampleCrosslinker (mM) Monomer (mM) (% bwoc) E 16 130 0.5 F 50 130 0.5 G 65130 0.5 H 82 130 0.5

Polymerization was stopped at a predetermined interval of about 24 hourswhere the w/o emulsion was filtered to produce the solid aramidecapsules. The aramide capsules were washed with 500 mL of a boratebuffer solution. The washed aramide capsules were vacuum dried producinga free flowing powder.

A cement slurry was formed having water, cement, and 3% bwoc of thearamide capsules. Any type of cement can be used in the cement slurry,including all Portland cements, any type of cement as classified by theAmerican Society for Testing and Materials (ASTM), such as Type I, II,III, or V, and any type of cement as classified by the AmericanPetroleum Institute (API), such as Class A, C, G, or H. Portland cementsare described in API specification for “Materials and Testing for WellCements,” API 10B-2 of the API. Following API standards the slurry wasblended at 4,000 revolutions per minute (rpm) for 15 seconds (s) andthen increased to 12,000 rpm for 35 s. The slurry was placed in arheometer (Anton Paar GmbH, Graz, Austria) to measure changes inviscosity over time.

The results were shown in FIG. 4. FIG. 4 is a graphical representation400 showing viscosity of the cement slurry having the encapsulant withinthe aramide capsule samples of varying monomer concentration. Thehorizontal axis represents concentration of the crosslinker in mM. Thevertical axis represents viscosity of the cement slurry in centipoise(cP). Square points 410 and the corresponding lines 412 representviscosities of cement slurries having Samples E-G collected at 0 minutesof mixing the slurry. Circular points 420 and the corresponding lines422 represent viscosities of cement slurries having Samples E-Gcollected at 10 minutes of mixing the slurry. Triangular points 430 andthe corresponding lines 432 represent viscosities of cement slurrieshaving Samples E-G collected at 20 minutes of mixing the slurry.Reverse-triangular points 440 and the corresponding lines 442 representviscosities of cement slurries having Samples E-G collected at 30minutes of mixing the slurry.

FIG. 4 shows that the viscosity of the cement slurry was dependent onthe amount of the crosslinker. FIG. 4 also shows that the permeability,and as a result the release rate of the encapsulant, can be controlledby the amount of the crosslinker added to the mixture. An increase inthe concentration of the crosslinker resulted in a decrease in membranepermeability.

EXAMPLE 5

A number of samples of aramide capsules were formed according to themethods described. The continuous solvent was a 4:1cyclohexane-chloroform blend. The surfactant was a 1.5% by volumesorbitan trioleate (Span-85®, Sigma-Aldrich®, St. Louis, Mo.). Thecontinuous phase included the continuous solvent and the surfactant. Thecrosslinker was 1,3,5-benzenetricarbonyl trichloride. The dispersedsolvent was water. The dispersed monomer was 1,6-diaminohexane. Thecement additive was the dispersant SAFC. The dispersed phase includedthe dispersed solvent, the dispersed monomer, and the cement additive.SAFC has a red color, and so acted as a dye or a signaling molecule. TheSAFC allowed measurements to be taken of the release rate from thearamide capsules.

The aramide capsules were prepared at room temperature. The dispersedphase included the dispersed monomer in an amount in mM according toTable 3. The dispersed phase included 0.5% bwoc of the SAFC encapsulant.The mixture was stirred for 15 minutes forming a w/o emulsion. After 15minutes of stirring, the crosslinker in an amount in mM according toTable 3 was added to the mixture at a rate of about 1.5 mL per minute.Stirring continued while the crosslinker was being added. Stirringmaintained the w/o emulsion.

TABLE 3 Amount of Amount of Amount of SAFC Crosslinker DispersedEncapsulant Sample (mM) Monomer (mM) (% bwoc) I 0 0 0.5 (freedispersant, no capsules in cement) J 20 130 0.5 K 50 130 0.5 L 80 1300.5

Polymerization was stopped at a predetermined interval of about 24 hourswhere the w/o emulsion was filtered to produce the solid aramidecapsules. The aramide capsules were washed with 500 mL of a diethylether and borate buffer solution. The washed aramide capsules werevacuum dried.

A cement slurry was formed having water, cement, and 3% bwoc of thearamide capsules. In addition to the cement slurries having aramidecapsules, a neat cement slurry was also formed having water and cement.Any type of cement can be used in the cement slurry, including allPortland cements, any type of cement as classified by ASTM, such as TypeI, II, III, or V, and any type of cement as classified by API, such asClass A, C, G, or H. Portland cements are described in API specificationfor “Materials and Testing for Well Cements,” API 10B-2 of the API.Following API standards the slurry was blended at 4,000 rpm for 15 s andthen increased to 12,000 rpm for 35 s. The slurry was placed in arheometer (Anton Paar GmbH, Graz, Austria) to measure changes inviscosity over time.

The results are shown in FIG. 5. FIG. 5 is a graphical representation500 showing viscosity of the cement slurry having aramide capsulesamples over time. The horizontal axis represents time in minutes. Thevertical axis represents viscosity of the cement slurry in cP. Emptycircular points 510 and the corresponding lines 512 representviscosities of the cement slurry having Sample I over time. Squarepoints 520 and the corresponding lines 522 represent viscosities of thecement slurry having Sample J over time. Triangular points 530 and thecorresponding lines 532 represent viscosities of the cement slurryhaving Sample K over time. Reverse-triangular points 540 and thecorresponding lines 542 represent viscosities of the cement slurryhaving Sample L over time. Filled circular points 550 and thecorresponding lines 552 represent viscosities of the neat cement slurryover time.

FIG. 5 shows that the viscosity of the cement slurry was dependent onthe amount of the crosslinker. FIG. 5 also shows that the permeability,and as a result the release rate of the encapsulant, can be controlledby the amount of the crossliner added to the mixture. An increase in theconcentration of the crosslinker resulted in a decrease in membranepermeability.

EXAMPLE 6

A capsule-based cement having aramide capsules was prepared. Examplearamide capsules include aramide capsules formed in Examples 1-5. Acement slurry was formed having water, cement, and 3% bwoc of thearamide capsules. Any type of cement can be used in the cement slurry,including all Portland cements, any type of cement as classified byASTM, such as Type I, II, III, or V, and any type of cement asclassified by API, such as Class A, C, G, or H. Portland cements aredescribed in API specification for “Materials and Testing for WellCements,” API 10B-2 of the API. Following API standards the slurry wasblended at 4,000 rpm for 15 s and then increased to 12,000 rpm for 35 s.

A neat cement was prepared. A cement slurry was formed having water andcement. Any type of cement can be used in the cement slurry, includingall Portland cements, any type of cement as classified by ASTM, such asType I, II, III, or V, and any type of cement as classified by API, suchas Class A, C, G, or H. Portland cements are described in APIspecification for “Materials and Testing for Well Cements,” API 10B-2 ofthe API. The slurry was blended at 4,000 rpm for 15 s, and blended at12,000 rpm for 35 s.

A latex-based cement was prepared. A cement slurry was formed havingwater, cement, 6% bwoc of a 50% latex solution, and 15% by weight of thelatex solution a stabilizer. Any type of cement can be used in thecement slurry, including all Portland cements, any type of cement asclassified by ASTM, such as Type I, II, III, or V, and any type ofcement as classified by API, such as Class A, C, G, or H. Portlandcements are described in API specification for “Materials and Testingfor Well Cements,” API 10B-2 of the API. Example latexes includecarboxylated latexes and carboxylated styrene-butadiene latexes. Theslurry was blended at 1,000 rpm for 35 s.

After mixing, each slurry was poured into a sample holder of anultrasonic cement analyzer (UCA, from Chandler Engineering, BrokenArrow, Okla.) for measuring confined compression strength. The UCA issuitable for curing cement slurries and conducting in situ testing ofcements at wellbore conditions. Each slurry was then placed into acuring chamber to start the measurement, where the cement remained for aperiod of about 72 hours to about 120 hours at about 350 deg. F. andabout 3,000 psi.

The results are shown in FIG. 6. FIG. 6 shows a graphical representation600 of unconfined compression strengths of cement samples formed inExample 6. Graphical representations 610, 620, 630 correspond to theunconfined compression strengths of the neat cement, the aramidecapsule-based cement, and the latex-based cement, respectively. Thevertical axis represents the unconfined compression strength in psi. Thehorizontal axis represents time in hours. As shown in FIG. 6, the neatcement exhibits an unconfined compression strength ranging from about3,500 psi to about 3,600 psi, at about 350 deg. F. for about 120 hours.The capsule-based cement exhibits an unconfined compression strengthranging from about 3,000 psi to about 3,400 psi, at about 350 deg. F.for about 120 hours. The latex-based cement exhibits an unconfinedcompression strength ranging from about 1,900 psi to about 2,200 psi, atabout 350 deg. F. for about 120 hours.

FIG. 6 shows that cement strength retrogression occurs significantly forthe latex-based cements compared to neat cement at wellbore conditions.On the other hand, cement strength retrogression does not significantlyoccur for the capsule-based cement, showing that the aramide capsulesand the cement additives within the capsules provide structuralintegrity to the cement.

Although the embodiments have been described in detail, it should beunderstood that various changes, substitutions, and alterations can bemade hereupon without departing from the principle and scope.Accordingly, the scope of the embodiments should be determined by thefollowing claims and their appropriate legal equivalents.

There various elements described can be used in combination with allother elements described here unless otherwise indicated.

The singular forms “a”, “an” and “the” include plural referents, unlessthe context clearly dictates otherwise.

Optional or optionally means that the subsequently described event orcircumstances may or may not occur. The description includes instanceswhere the event or circumstance occurs and instances where it does notoccur.

Ranges may be expressed here as from about one particular value to aboutanother particular value and are inclusive unless otherwise indicated.When such a range is expressed, it is to be understood that anotherembodiment is from the one particular value to the other particularvalue, along with all combinations within said range.

As used here and in the appended claims, the words “comprise,” “has,”and “include” and all grammatical variations thereof are each intendedto have an open, non-limiting meaning that does not exclude additionalelements or steps.

What is claimed is:
 1. A method for encapsulating a cement additive foruse in a wellbore, the method comprising the steps of: mixing acontinuous solvent and a surfactant to produce a continuous phase;mixing a dispersed solvent, a dispersed monomer, and the cement additiveto produce a dispersed phase, where the dispersed solvent and thecontinuous solvent are immiscible; mixing the continuous phase and thedispersed phase to form a mixture having an emulsion such that thedispersed phase is dispersed as droplets in the continuous phase, wherean interface defines the droplets of the dispersed phase dispersed inthe continuous phase; adding a crosslinker to the mixture; allowing anaramide polymer to form on the interface of the droplets, such that thearamide polymer forms a semi-permeable membrane around a core, where thecore contains the dispersed phase, such that the semi-permeable membranearound the core forms an aramide capsule; allowing the aramide capsuleto settle from the mixture; and separating the aramide capsule from themixture using a separation method.
 2. The method of claim 1, where thedispersed solvent is selected from the group consisting of water,ethanol, methanol, and combinations of the same.
 3. The method of claim1, where the dispersed monomer comprises an amine group.
 4. The methodof claim 3, where the dispersed monomer is selected from the groupconsisting of ethylenediamine, meta-phenylenediamine,para-phenylenediamine, hexamethylenediamine, and combinations of thesame.
 5. The method of claim 1, where the continuous solvent is selectedfrom the group consisting of oil, mineral oil, cyclohexane, chloroform,and combinations of the same.
 6. The method of claim 1, where thecrosslinker is selected from the group consisting of1,3,5-benzenetricarbonyl trichloride, sebacoyl chloride, andcombinations of the same.
 7. The method of claim 1, where the cementadditive is water-soluble and is selected from the group consisting ofsealing reagents, anti-gas migration additives, high-temperatureretarders, fluid-loss additives, accelerators, superplasticizers, andcombinations of the same.